Title : Defect can adjust the band gap of solar cell semiconductor CuInS2

As one kind of thin film solar cell semiconductors, CuInS₂ with chalcopyrite structure has already become a hot research target in the realm of solar cell, due to many advantages and excellent properties. It is found in experiment that the emission wavelength of nanocrystal can be changed by controlling the [Cu]/[In] molar ratio. This discovery has paved the road for manufacturing wavelength-adjustable lasers. However, there lacks in theoretical explanation of such phenomena up until now. In the present work, defect-complexes on the electronic structure of CuInS₂ is investigated by means of first-principle method based on density functional theory. Two defect structures and realistic CuInS₂ are chosen, in order to have a look at the influences of defect-complexes on electronic structure and optical properties. Both PBE pseudopotential and hybrid functional are used to compute the band gap. It is found that these three compounds belong to semiconductors. Band gaps become smaller and smaller with the increase of [Cu]/[In] molar ratio, which is consistant with previous experimental results. The top of valence gap rises and the band gap becomes narrower and narrower if the concentration of Cu increases in the semiconductor. These theoretical findings can help elucidate the effects of [Cu]/[In] molar ratio on optical properties of chalcopyrite CuInS₂, which provides a physical mechanism of adjusting semiconductors’ emission wavelength in the experiment.

Keywords: Chalcopyrite, First-principles, defect-complex

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